This invention relates generally to a tie rod assembly and more particularly to an adjustable tie rod assembly for a steering linkage system including types having several ball joints such as those generally known as a parallelogram steering linkage system.
A parallelogram steering linkage system comprises a relay rod that is connected to the frame or chassis of an automobile by two pivoting members, such as a pitman arm and an idler, in a parallelogram arrangement so that the relay rod savings back and forth laterally in response to steering inputs from the steering wheel of the automobile via a steering gear. The pivoting members are connected to the relay rod by ball joints. The opposite end portions of the relay rod are each connected to a steering knuckle by a tie rod assembly. The tie rod assemblies are connected to the relay rod by ball joints. The steering knuckles turn the front wheels of the automobile to steer the automobile in response to movements of the relay rod and the tie rods that connect the relay rod to the steering knuckles. The steering knuckles are connected to suspension members by ball joints. Some parallelogram steering linkage systems also include a drag link for moving the relay rod. These systems and other systems having several ball joints are sensitive to ball joint friction.
Wheel toe is the angular position of the front wheel with respect to a vertical longitudinal plane of the vehicle at zero steering input. Ideally the wheel toe is zero so that the vehicle tracks in a straight line when the steering input is zero. The wheel toe for each front wheel is adjusted by adjusting the length of the associated tie rod assembly.
One known type of adjustable tie rod assembly has low friction ball joints at each end and a dual jam nut arrangement for adjustment. This dual jam nut arrangement which is shown in FIG. 4 of the patent drawing, comprises a tie rod that has oppositely threaded ends. Each threaded end is screwed into an internally threaded portion of a ball joint housing. The tie rod also carries a jam nut at each end that is tightened against the adjacent housing to maintain the depth of the threaded end in the housing. The length of the tie rod assembly is adjusted while connected in the steering linkage system by loosening the two jam nuts and turning the tie rod with respect to the two ball joint housings at the respective ends of the tie rod. The two jam nuts are then tightened down after the adjustment is made to maintain the adjustment.
A disadvantage of the dual jam nut type adjustable tie rod assembly is that two jam nuts must be loosened and then retightened to adjust the length of the assembly. Moreover the two jam nuts must be turned in opposite directions for loosening and then turned in opposite directions for retightening. This characteristic makes manual adjustment tedious, time consuming and complicated. Furthermore a machine for automatically adjusting the dual jam nut type adjustable tie rod assembly is not available.
Another known type of adjustable tie rod assembly has a high friction, in-line ball joint at one end and a single jam nut arrangement for adjustment. This adjustable tie rod assembly, shown in FIG. 3 of the patent drawings is used in connection with rack and opinion steering systems that can tolerate high friction ball joints. This rack and pinion type adjustable tie rod assembly comprises a tie rod that has a concentric ball at one end and external threads at the opposite end. The concentric ball is pivotally mounted in an axially oriented housing of the steering rack to form a high friction in-line ball joint at one end of the tie rod. The threaded end of the tie rod is screwed into an internally threaded portion of the housing of an angled ball joint at the opposite end of the tie rod. The tie rod also carries a single jam nut that is tightened against the housing of the angled ball joint to maintain the depth of the threaded end in the housing. The length of the tie rod assembly is adjusted while connected in the rack and pinion steering system by loosening the single jam nut and turning the tie rod with respect to the two ball joint housings at opposite ends of the tie rod. The jam nuts is then tightened down after the adjustment is made.
The single jam nut arrangement simplifies manual adjustment in comparison to the dual jam nut arrangement. Machines are also available for automatically adjusting the single jam nut type adjustable tie rod assembly. However, the rack and pinion type adjustable tie rod assembly has several disadvantages. One disadvantage is that the in-line ball joint formed by the concentric ball of the tie rod is heavily preloaded to resist steering forces transmitted to the tie rod and to eliminate lash in the steering linkage system. This results in high friction in the in-line ball joint and increased steering effort. Another disadvantage is that as a practical matter, the ball end of tie rod must be connected to the end of the adjoining link which limits the application of this type adjustable tie rod assembly. Because of these disadvantages the concentric ball, single jam nut design is not feasible for all types of steering linkage systems. For instance the design is not feasible for use in parallelogram steering linkage systems which do not tolerate high friction ball joints very well. The design is also not feasible for use in steering linkage systems where the tie rod is connected to the relay rod at an inboard position, such as in the case of parallelogram steering linkage systems that are commonly used in light trucks.